1. Field of the Invention
The present invention relates to a nitride semiconductor laser device including a semiconductor multilayer structure made of group III nitride semiconductors.
2. Description of Related Art
Group III-V semiconductors employing nitrogen as a group V element are called “group III nitride semiconductors”, and typical examples thereof include aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN), which can be generally expressed as AlXInYGa1-X-YN (0≦x≦1, 0≦Y≦1 and 0≦X+Y≦1).
Short wavelength laser sources such as blue and green laser sources are increasingly employed in the fields of high-density recording in optical disks represented by a DVD, image processing, medical instruments, measuring instruments and the like. Such a short wavelength laser source is constituted of a laser diode employing GaN semiconductors, for example.
A GaN semiconductor laser diode is manufactured by growing group III nitride semiconductors on a gallium nitride (GaN) substrate by metal-organic vapor phase epitaxy (MOVPE). More specifically, an n-type cladding layer, an n-type guide layer, a light emitting layer (active layer), a p-type guide layer, a p-type electron blocking layer, a p-type cladding layer and a p-type contact layer are grown on the GaN substrate by the metal-organic vapor phase epitaxy, to form a semiconductor multilayer structure consisting of these semiconductor layers. For example, the n-type cladding layer is formed by a single AlGaN film, or has an AlGaN/GaN superlattice structure. The n-type guide layer is made of InGaN or GaN. The light emitting layer has a multiple quantum well structure including quantum well layers made of InGaN. The p-type guide layer is constituted of InGaN or GaN. The p-type electron blocking layer is constituted of AlGaN. The p-type cladding layer is formed by a single AlGaN film, or has an AlGaN/GaN superlattice structure. The p-type contact layer is constituted of AlInGaN.
According to this structure, the light emitting layer emits light by recombination of electrons and positive holes injected from the n-type layer and p-type layer respectively. This light is confined between the n-type cladding layer and the p-type cladding layer, and is propagated in a direction orthogonal to a stacking direction of the semiconductor multilayer structure. Cavity end faces are formed on both ends in the propagation direction, so that the light is resonantly amplified while repeating induced emission between the pair of cavity end faces and partially emitted from the cavity end faces as laser beams.